Each year the western and southern pine beetles (Dendroctonus brevicomis LeConte and Dendroctonus frontalis Zimm) do enormous amounts of damage to the pine forests of North America. Therefore, a means of controlling these pests is highly desirable.
The mass attacks on host trees by these insects is known to be guided at least in part by pheromones elicited by the insects. These pheromones act as aggregating agents to attract other beetles of the species to a food supply and to mating opportunities. Exploitation of the insects reliance upon an aggregation pheromone to bring the sexes together offers intriguing possibilities for insect control.
The pheromones initially direct the insects to weakened trees which they attack in mass and kill before moving on to destroy healthier trees. Additionally, the pheromones assure a high concentration of beetles in a relatively confined area and hence increase the chances of successful mating.
Pheromones have been used successfully in traps to control the explosive growth of Ips typographus in Norway and Sweden. In these countries, the insect pheromone was dispersed in small quantities from plastic tubes placed in the infested area. The insects were attracted inside the tubes which were constructed in such a way that they could not escape.
This procedure, however is not totally satisfactory for a number of reasons. The principal reason is that a large number of traps are required and their successful dispersion in a target area requires the work of many people.
In accordance with this invention, synthetic pheromones are provided which block or destroy the beetles pheromone receptor site so that the affected insect is no longer attracted to other beetles by the natural pheromone. The proximate effect is that the beetles are dispersed rather than concentrated. The ultimate effects are that the beetles feed on a large number of trees without lethal effects on any one, and the number of opportunities for successful mating are greatly reduced. The insect population is not destroyed. Instead, it is controlled. This is important because the insects contribute to the ecological balance of the forest. Their complete elimination would concurrently remove a valuable food source for the bird population.